Optical Signal to Noise Ratio (OSNR) is a ratio of signal power in a channel to noise power in a specific bandwidth range. OSNR indicates the level of noise in the signal, and is one of important technical indicators for optical performance monitoring.
Generally, OSNR is measured by out-of-band monitoring method based on an optical spectrum analyzer (OSA), which is recommended by ITU-T G.697. This method is characterized in that OSNR is calculated by estimating noise in channels with interchannel noise, and is widely used since it is easy and does not affect service.
This OSNR measuring method based on spectrum analysis has the following disadvantage: due to the factors such as mechanical adjustment in OSA or external environment change and so on, its setting resolution may be different from its actual resolution, which results in low precision for measuring OSNR based on the spectrum method.